1. Field Of The Invention
This invention relates generally to systems for gravel packing a production zone of a well, and more particularly, to a retrievable gravel packer for use in such a system.
2. Description Of The Prior Art
Unconsolidated formations, particularly those containing loose sands and sandstone strata, present constant problems in well production due to migration of loose sands and degraded sandstone into the well bore as the formation deteriorates under the pressure and flow of fluids therethrough. This migration of particles may eventually clog the flow passages in the production system of the well, and can seriously erode the equipment. In some instances, the clogging of the production system may lead to a complete cessation of flow, or killing of the well.
One method of controlling sand migration into a well bore consists of placing a pack of gravel on the exterior of a perforated or slotted liner or screen which is positioned across an unconsolidated formation to present a barrier to the migrating sand from that formation while still permitting fluid flow. The gravel is carried to the formation in the form of a slurry, the carrier fluid being removed and returned to the surface. The proper size of gravel must be employed to effectively halt sand migration through the pack, the apertures of the liner or screen being gauged so that the gravel will settle out on its exterior, with the slurry fluid carrying the gravel entering the liner or screen from its exterior and being circulated back to the surface.
Prior to effecting the gravel pack, drilling mud and other contaminants may be washed from the well bore, and the formation treated. Commonly employed treatments include acidizing to dissolve formation clays, and injecting stabilizing gels to prevent migration of formation components and formation breakdown prior to packing.
Subsequent to effecting the gravel pack, a reverse circulation technique may be utilized to remove remaining gravel laden slurry from the operating string utilized to conduct the slurry. With such a reverse circulation technique, the direction of circulation is reversed and a clean fluid is pumped down the path previously utilized for returning the slurry fluid, and the remaining gravel laden slurry will be forced back up the path originally used to conduct the gravel laden slurry down to the well.
A typical prior art retrievable gravel packer is disclosed in U.S. Pat. No. 4,049,055 to Brown and assigned to the Brown Oil Tools, Inc. Brown discloses a hydraulic set retrievable gravel packer 10 which has its expandable packing element, its upper and lower packing shoes, its slip elements, and its upper and lower wedges arranged in a fashion somewhat similar to that of the gravel packer of the present invention. The Brown gravel packer differs substantially from that of the present invention in several areas. One of the most significant distinctions is that Brown does not disclose a non-rotational connecting means connected between the mandrel and each of the upper and lower shoes and upper and lower wedges for preventing rotation of those elements relative to the mandrel. Additionally, the releasing mechanism utilized in the Brown gravel packer is substantially different from that of the present invention.
Another typical prior art retrievable well packer is shown in U.S. Pat. No. 3,678,998 to Cockrell et al. and assigned to Baker Oil Tools, Inc. The Cockrell et al. packer is a wireline set packer. Although the components of the Cockrell et al. packer are arranged in a considerably different manner than is the present invention, Cockrell et al. does disclose in FIG. 1c thereof pins 67 and 69 slidably received in a slot 68, which appear to hold the mandrel of the packer against relative rotation relative to the upper and lower packer shoes and the upper wedge. There does not, however, appear to be any non-rotational connection between the mandrel and the lower wedge.
U.S. Pat. No. 3,987,854 to Callihan et al., and assigned to Baker Oil Tools, Inc., appears to be in some aspects similar to the disclosure of U.S. Pat. No. 3,678,998 just discussed above, although it does not disclose the use of pins received in slots as did U.S. Pat. No. 3,678,998. The Callihan et al. U.S. Pat. No. 3,987,554, however, is disclosed in the context of a hydraulically set gravel packing system.
Another typical prior art hydraulically set gravel packer is disclosed in U.S. Pat. No. 4,180,132 to Young, and assigned to Otis Engineering Corporation.